Reference Signal Reception and Cqi Computation Method and Wireless Communication Apparatus

1. A communication apparatus comprising: a receiver, which, in operation, receives a first reference signal that is mapped in a subframe and transmitted to the communication apparatus compliant with a first communication system, and receives a second reference signal that is mapped in all subframes and transmitted to the communication apparatus and another communication apparatus compliant with a second communication system; and circuitry, which, in operation, computes a channel quality indicator (CQI) based on the received first reference signal and the received second reference signal, wherein the first reference signal is not transmitted in a subframe where a transmission of the first reference signal collides with a transmission of a physical broadcast channel (PBCH) or system information block 1 (SIB1).

2. The communication apparatus according to claim 1 , wherein said receiver, in operation, receives a third reference signal that is mapped and transmitted on a resource block upon which data is mapped, and said circuitry, in operation, demodulates the data based on the received third reference signal.

3. The communication apparatus according to claim 2 , wherein the third reference signal is a UE-specific reference signal.

4. The communication apparatus according to claim 1 , wherein the second reference signal is a cell-specific reference signal.

5. The communication apparatus according to claim 1 , wherein the second reference signal is used for demodulating the PBCH or a downlink control channel.

6. The communication apparatus according to claim 1 , wherein the first reference signal is mapped such that a number of symbols of the first reference signal per resource block is less than a number of symbols of the second reference signal per resource block.

7. The communication apparatus according to claim 1 , wherein a maximum number of antenna ports of a base station compliant with the first communication system is greater than a maximum number of antenna ports of a base station compliant with the second communication system.

8. The communication apparatus according to claim 1 , wherein the first communication system is a LTE-Advanced system, and the second communication system is a LTE system.

9. The communication apparatus according to claim 1 , wherein the first reference signal is mapped in a set period.

10. The communication apparatus according to claim 1 , wherein the first reference signal is mapped with an interval, which is the same as (i) an interval of retransmissions in a HARQ process or a number of HARQ processes, (ii) an integer multiple of an interval of retransmissions in a HARQ process or an integer multiple of a number of HARQ processes, or (iii) 1/N of an interval of retransmissions in a HARQ process or 1/N of a number of HARQ processes, where N is a positive integer.

11. The communication apparatus according to claim 1 , wherein the first reference signal is mapped in a same period as a period in which a CQI is reported, or in a period which is an integer multiple of a period in which a CQI is reported.

12. The communication apparatus according to claim 1 , wherein the first reference signal is mapped in a same period as a period of semi-persistent scheduling (SPS) transmission, or in a period which is 1/N of a period of SPS transmission, where N is a positive integer.

13. The communication apparatus according to claim 1 , wherein the first reference signal is a cell-specific reference signal.

14. The communication apparatus according to claim 1 , wherein the first reference signal is a channel state information-reference signal (CSI-RS).

15. A communication method comprising: receiving a first reference signal that is mapped in a subframe and transmitted to the communication apparatus compliant with a first communication system; receiving a second reference signal that is mapped in all subframes and transmitted to the communication apparatus and another communication apparatus compliant with a second communication system; and computing a channel quality indicator (CQI) based on the received first reference signal and the received second reference signal, wherein the first reference signal is not transmitted in a subframe where a transmission of the first reference signal collides with a transmission of a physical broadcast channel (PBCH) or system information block 1 (SIB1).